1. Technical Field
The present invention relates to an optical film, and particularly to an optical film for a backlight module and a backlight module using the optical film.
2. Description of the Related Art
A backlight module is for providing a plane light source to a liquid crystal display panel (LCD panel). The backlight module may be distinguished into a direct type backlight module and an edge type backlight module according to the incident direction of light rays. The edge type backlight module usually uses a light guide plate to convert the light rays provided by a light source into the plane light source. Moreover, to promote luminance and uniformity of the plane light source, at least an optical film is disposed above a light emitting surface of the light guide plate.
FIG. 1 is a schematic view of a conventional optical film. Referring to FIG. 1, a plurality of V shape protrusions 110 disposed side by side is disposed at a light incident side 102 of the conventional optical film 100. Each of the V shape protrusions 110 has a light incident surface 112 and a reflection surface 114, and the light incident surface 112 and the reflection surface 114 are flat surfaces. Light rays 50 emitting from a light emitting surface of a light guide plate (not shown) are inclined light rays. The light rays 50 are incident into the V shape protrusions 110 from the light incident surfaces 112. Afterward, the light rays 50 are reflected by the reflection surfaces 114 and then emit from a light emitting side 104 of the optical film 1 00.
FIG. 2 is a luminance distribution diagram of the light rays emitting from the optical film of FIG. 1, wherein the transverse axis of the luminance distribution diagram represents a light emitting angle and the vertical axis of the luminance distribution diagram represents luminance. Referring to FIGS. 1 and 2, in the conventional optical film 100, the reflection surfaces 114 may reflect the light rays 50 and let the light rays 50 emit from the light emitting side 104, but the diverging angle of the light rays 50 is not converged. Therefore, the luminance of the backlight module is reduced, especially in the positive direction. In other words, the luminance at 0 degree is low.
FIG. 3 is a schematic view of another conventional optical film. Referring to FIG. 3, a plurality of V shape protrusions 110′ disposed side by side is disposed at a light incident side 102′ of the conventional optical film 100′. Each of the V shape protrusions 110′ has a light incident surface 112′ and a light reflection surface 114′, each of the light incident surfaces 112′ includes a flat surface portion 112a and a curved surface portion 112b, and each of the reflection surfaces 114′ includes a flat surface portion 114a and a curved surface portion 114b. The light rays 50 emitting from a light emitting surface of a light guide plate (not shown) are inclined light rays. The light rays 50 are incident into the V shape protrusions 110′ from the light incident surfaces 112′. Afterward, the light rays 50′ are reflected by the reflection surfaces 114′ and then emitting from a light emitting side 104 of the optical film 100′.
FIG. 4 is a luminance distribution diagram of the light rays emitting from the optical film of FIG. 3, wherein the transverse axis of the luminance distribution diagram represents a light emitting angle and the vertical axis of the luminance distribution diagram represents luminance. Referring to FIGS. 3 and 4, in the conventional optical film 100′, the diverging angle of the light rays 50 reflected by the curved surface portions 114b of the reflection surfaces 114′ is converged, so the luminance of the backlight module is increased in the positive direction. However, the diverging angle of the light rays 50 reflected by the flat surface portions 114a of the reflection surfaces 114′ is not converged, so the luminance of the backlight module is not greatly increased in the positive direction.
Other objectives, features and advantages of the present invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention.